RECLAIMING OVERFLOWED LANDS IN MISSISSIPPI. 
APPUCATION OF RUN-OFF RESULTS. 
25 
The following is a summary of the results obtained for the three 
drainage areas discussed: 
Drainage area. 
Probable 
run-off. 
Square miles. 
3,120 
1,200 
100 
Second-feet per 
square mile. 
24.0 
31.5 
93.7 
In order to utilize these results as a basis for determining run-ojff 
from other areas, it is necessary to incorporate them into a formula 
which will give the probable run-off from any desired drainage area. 
A formula of the Murphy type seems best adapted to the use of the 
above data. 
The Murphy formula is 
Q = 
46790 
if +320 
+ 15 
in which Q equals the discharge in second-feet from each square 
mile, and M the watershed area in square miles. Adopting a general 
formula of the above form, viz., 
the values of X, Y, and Z were derived by substituting for Q and M 
the following values obtained for the Big Black watershed: 
Where M= 100, Q = 95 
Where Ji = 1200, Q = 32 
Where Jf= 3000, Q = 24 
Substituting the above values, and solving, the following formula 
was obtained: 
18700 
Q 
M+U4: 
+ 18 
For convenience in the use of this equation its curve has been 
platted (fig. 5). It is behevsd that this curve represents the max- 
imum rate of run-off that may be expected under improved condi- 
tions, and the design of all levee improvements has been based upon 
it, although no rate of run-off greater than 90 second-feet per square 
mile has been used. 
If a levee system be insufficient to care for the flood conditions, 
great damage may be done to the land presumed to be protected 
and to the levees themselves ; great care should therefore be taken to 
provide for maximum run-off conditions. On the other hand, if a 
